Flow control valves are well known in irrigation systems. They control the flow of pressurized water through a pipe to turn sprinklers connected to the pipe on and off. Such valves are often remotely controlled by control signals sent from an automated irrigation controller. For example, the controller might send an electric actuating signal to a solenoid that is part of the valve to allow the valve to open.
Various prior art valves use a resilient diaphragm which engages the top of a valve seat for controlling fluid flow through the valve body. The diaphragm is often "pressure balanced" so that inlet fluid pressure is seen on both the top and bottom sides of the diaphragm. The valve is opened by bleeding fluid pressure away from the top side of the diaphragm. This allows the fluid inlet pressure acting on the bottom side of the diaphragm to lift the diaphragm up off the valve seat, thereby opening the valve.
In some cases, the closing force on the diaphragm is achieved by a pressure differential acting on the diaphragm due to the shape of the diaphragm and the proportioning of the top and bottom sides thereof. In other words, the inlet pressure on the top side of the diaphragm has a greater surface area to act against than the surface area on the bottom side of the diaphragm, thus providing a net downward force on the diaphragm urging the diaphragm into engagement with the valve seat. U.S. Pat. Nos. 3,022,039 to Cone and 3,240,128 to Wilson disclose such a valve.
One difficulty with this construction is the inability of the diaphragm to properly seat at relatively low pressure flows, particularly when the diaphragm has been fully opened and is off the valve seat by a considerable distance. In this condition, the differential pressure developed across the diaphragm may not be large enough to cause the diaphragm to reseat. If this happens, the valve will remain open when it should be closed. This is obviously undesirable.
Some valves of this type have used biasing springs acting against the diaphragm to provide a reliable closing force to seat the diaphragm under all fluid pressures for which the valve is rated. However, this is undesirable since the use of extra components, such as a spring, increases the complexity, and hence the expense of manufacturing, the valve. U.S. Pat. No. 3,495,804 to Muller et al discloses a valve of this type having a closing spring acting on the valve diaphragm.
Keeping in mind that valves of this type are typically built to work over a range of flow pressures, from as low a pressure as possible to as high a pressure as possible, it is necessary to reinforce the central portion of the diaphragm to prevent distortion under higher pressure flows. Undue distortion would prevent the diaphragm from properly seating against the valve seat, again causing the valve to leak.
Any reinforcing member used on the diaphragm needs to be securely fixed to the diaphragm to prevent separation therefrom. This is often accomplished by molding the reinforcing forcing member into the diaphragm when the diaphragm is manufactured. However, this is not a desirable technique as it requires proper positioning of the reinforcing member in the mold cavity, which is difficult to do on a consistent basis. In addition, the cycle time for manufacturing the diaphragm is significantly increased and the rejection rate for finished diaphragms may also be increased due to problems in adhering the reinforcing member to the diaphragm.